In the field of scuba diving, it is well known that at times it is difficult for a diver to find his or her way back to a dive boat, to re-join a companion or buddy diver, or to identify and locate a designated underwater object. This is especially true when underwater visibility is poor.
Prior art underwater location devices are typically combined with a communication device. For example, U.S. Pat. No. 3,181,115 to Wainwright discloses a device that uses a directional hydrophone to locate a desired object (i.e., for homing).
U.S. Pat. No. 3,469,231 to Geiling et al. discloses an apparatus for determining a direction of a signal by using a directional hydrophone along with an omni-directional hydrophone to detect the existence of the signal itself. Distance may be determined by measuring the power of the received signal.
U.S. Pat. No. 3,587,038 to Massa discloses a device which uses a directional hydrophone to determine the direction of a signal, while distance is determined by measuring the power of the received signal.
U.S. Pat. No. 3,792,424 to akatsuji et al. discloses a device for detecting the position of a movable object under-water. The device disclosed in Nakatsuji et al. has at least three ultrasonic receivers for detecting a position of the object under-water and that operate in conjunction with an ultrasonic transmitter mounted on the movable object. Distance between the device and the movable object is estimated by measuring the round trip time of a signal transmitted by the device. However, a large distance between hydrophones (i.e., between the ultrasonic receivers of the device and the ultrasonic transmitter of the object) is required to obtain an accurate measure of distance. Moreover, the size of the device makes it impractical for carrying by a scuba diver.
U.S. Pat. No. 5,570,323 to Prichard et al. discloses a device for determining a direction toward and a distance to a dive boat. The direction is estimated by measuring the angle of a received signal by using an array of three omni-directional hydrophones. The distance is estimated by measuring the round trip time of a signal transmitted and received by the device.
U.S. Pat. No. 5,666,326 to Holzschuh discloses a homing device which uses a single hydrophone located in close proximity to a diver's torso. The acoustic discontinuity between the diver's torso and the device provide the required directional sensitivity. However, the accuracy of the obtained directional sensitivity is low. Moreover, in order to operate the device, the diver must be in a vertical position, which is not typical for underwater swimming.
U.S. Pat. No. 5,784,339 to Woodsum et al. discloses a method for identifying the location of a diver or submersible object with respect to another diver or submersible object or surface craft. This is done by using an array of directional hydrophones to measure the angles of reception of a signal. The distance is estimated by measuring the round trip time of an interrogation signal transmitted and received by the diver.
All of the above-described prior art devices and methods are based on directional hydrophones or an array of omni-directional or directional hydrophones. It is generally known in the art that the directionality of a directional hydrophone depends on its size. Better directionality requires larger hydrophones. Moreover, an omni-directional hydrophone is required to determine the existence of a received signal. The prior art devices and methods discussed above provide relatively low accuracy and require relatively large directional hydrophones, in addition to requiring an omni-directional hydrophone. Consequently, the prior art devices and methods are generally not suitable or convenient for carrying by a scuba diver. Finally, none of the devices and methods disclosed above provide the azimuth (an angle in degrees relative to a fixed point, such as magnetic North) toward the object to be located.
U.S. Pat. No. 5,463,598 to Holland discloses a method based on the Doppler effect for locating a diver or object in the water from a vessel. A receiver aboard the vessel acquires an acoustic signal transmitted by a hydrophone on the diver or object and compares the frequency of the received signal with an internal reference to determine the amount by which the received signal is Doppler shifted. This frequency shift is translated to velocity of the vessel which is displayed in knots on an illuminated red or green bar graph, with red indicating velocity away from and green indicating velocity toward the diver or object. If the vessel is piloted so as to maximize the green bar graph display, the vessel proceeds directly toward the diver or object. This type of apparatus makes it possible to find a diver or object in water only from a vessel. Moreover, the magnitude of the speed of the vessel must be kept constant during a search. Finally, the method disclosed by Holland does not provide the azimuth toward the object to be located.
Yet another object of the present invention is to provide an underwater communication method, device, and system capable of determining a direction from and a distance to an object using a single omni-directional hydrophone and further capable of bi-directional communication and display of textual messages.
Still another object of the present invention is to provide an underwater communication method, device, and system which can remotely cause an underwater device to transmit a locating signal to assist in locating an injured or otherwise disabled diver.